1. The invention relates to an automatic tapping device for use on mechanical presses such as eccentric presses or crankshaft-operated deep-drawing presses.
2. Description of the Prior Art
Cheap metal parts are currently manufactured on mechanical stamping presses, for example eccentric presses, by means of multiple tools which, at a first station, punch holes in a sheet metal strip and, at a subsequent station, cut out parts, so that the parts fall separately almost finished from the machine. Often a large number of operations are carried out, for example, bending, raising of fastening lugs, and stamping operations at the edges of the holes (so called "staved") with a view to the tapping of said holes subsequently.
It is precisely to this operation of tapping the holes to which the present invention relates. Often, for this purpose, the parts are retaken to cause them to pass over a tapping machine, which considerably lowers the efficiency, and since it is necessary, in fact, to take more time to pick up the parts and tap them than to stamp them out. Working with presses is particularly economical, since one or several parts are delivered on each stroke of the press, which is why efforts have already been made to gain a part of this advantage by carrying out the tapping of the parts on the press itself, immediately after their punching, before they are cut out, which avoids picking up the parts again to tap them.
To carry out this type of operation, it has been proposed to use a device which includes a rotary taping-bit holder, which is mounted on the tool-holder of the press, the driving of the tapping-bit holder spindle in rotation being ensured from a rack and pinion system actuated by the vertical movement of the tool-holder. Such a device has, for example, been described in German Pat. No. 357 354 issued Nov. 30, 1982 in the name of ALBRECHT.
However, devices of this type generally necessitate modification of certain elements of the press, which constitutes a drawback.
It has also been proposed to use the approach movement of the two plates of the press to rotate one of the two elements, the screw or the nut, of a reversible screw and nut system and to drive in rotation, from this element, a rotary tapping-bit holder spindle.
Such devices have been described, for example, in U.S. Pat. No. 3,579,687 in the name of Hoshi, et al or in U.S. Pat. No. 3 162 873 in the name of OHME.
However these devices are of complicated structure and of great height, with numerous sliding movable parts, which necessitates a very heavy and hence expensive construction. In fact, the whole mechanism constituted particularly by the reversible screw/nut system, by the rotary tapping-bit holder spindle and by the gear transmission between this system and this spindle was mounted in a single tool-block mounted on the upper tool-holder of the press. This single tool-block hence had to include a sliding plate, with guiding columns of large cross-section, and required accurate, and hence expensive construction to avoid any risk of jamming.
In addition, the withdrawal of the tapping-bit, on the re-ascent of the press, could not be actuated positively by the re-ascent of the press plate. Powerful return springs had to be provided, wound around the aforesaid columns, to push back the sliding plate of the single tool-block and effect the driving in the reverse direction of the screw/nut system and of the tapping-bit holder. The necessity for these return springs again rendered the construction of the device heavier and more expensive.
It is as object of the present invention to provide a device for tapping on a press of the aforementioned type, but which is much simpler and less expensive than the devices known hitherto.
Other objects and advantages of the invention will be apparent from the description which follows.